use Regexp::List qw( );
my $re = Regexp::List->new(modifiers => 'i')
                     ->list2re( map lc($hash{$_}[0]),
                                keys %hash
                              );

# or:
# my ($re) = map qr/$_/i,
#            join '|',
#            map quotemeta(lc($hash{$_}[0])),
#            keys %hash;


while (my $cur_line = <$fh_log>) 
{ 
   while ($cur_line =~ /($re)/g)
   { 
      my $table = lc($1);
      if ($tables{$table}) {
         # Count up how many times this table is referenced. 
         $table_stats{$table}++; 
         $table_refs++;
      } 
   } 
}